(a) Field of the Disclosure
The present disclosure relates to a method for fabricating a semiconductor device including silicon carbide (SiC).
(b) Description of the Related Art
With the recent trend toward large-sized and large-capacity application apparatuses, a power semiconductor device having a high breakdown voltage, a high current capacity, and high-speed switching characteristics has become necessary.
Accordingly, much research and development is being conducted on MOSFETs (metal oxide semiconductor field effect transistors) using silicon carbide (SiC), instead of conventional MOSFETs using silicon. Particularly, there is a great deal of development of vertical trench MOSFETs.
In a vertical trench MOSFET, a trench is formed, and then a gate insulating film is formed on the bottom and sides of the trench. A gate insulating film used for a vertical trench MOSFET using silicon carbide is generally a silicon dioxide (SiO2) film formed by oxidizing silicon carbide by oxygen, steam, etc.
Silicon carbide reacts with oxygen, steam, and other gases containing oxygen to form a silicon dioxide film on a surface. Specifically, silicon reacts with oxygen atoms to form a silicon dioxide film, and carbon atoms react with oxygen whereby some of the carbon atoms are vaporized into carbon monoxide (CO) and carbon dioxide (CO2) thereby disappearing, and the remaining carbon atoms are left at the interface between the silicon dioxide film and the silicon carbide.
After forming a gate insulating film, doped polysilicon or a metallic material is deposited in the trench to form a gate electrode.
Anisotropy of the physical properties of silicon carbide exists depending on the orientation of a crystal plane, and the oxidation rate of silicon carbide differs depending on the crystal plane. Thus, in most currently available silicon carbides, a thick gate insulating film, i.e., a silicon dioxide film, is grown on sides of the trench rather than on the bottom of the trench. If there is a relatively large difference in the oxidation rate depending on the crystal orientation, this has a serious adverse effect on the operating characteristics of a vertical trench MOSFET using silicon carbide.
Even when a gate insulating film is formed by a thin film formation process rather than by an oxidation process in order to overcome this issue, the interface characteristics between the gate insulating film and silicon carbide are not good This causes many problems including a degradation of the mobility of a vertical trench MOSFET device using silicon carbide, variations in threshold voltage, etc.
The above information disclosed in this Background section is only for enhancement of the understanding of the background of the disclosure and therefore it may contain information that is not prior art.